Antenna system



Dec. 30, 1947. w. M. HURST ANTENNA SYSTEM Filed April 3, 1945 k v a:

INVENTOR. WILLlAM M. HURST M/ m ATTORNEY Patented Dec. 30, 1947 PATENT orr ca ANTENNA SYSTEM William M. Hurst, Douglaston, N. Y., assignor,

by mesne assgnments,

to Hazeltine Research,

Inc., Chicago, 11]., a corporation of Illinois Application April 3, 1945, Serial No. 586,348

10 Claims. (Cl. 174-12) The present invention relates to antenna systems and, particularly, to such a system suitable for use with aircraft wherein the antenna system during operation is subjected to variations of atmospheric pressure resulting from the flight of the aircraft between low to high altitudes.

For certain applications, it is desirable to provide on aircraft one or more short, vertical, relatively rigid antennas. It has heretofore been conventional to support such antennas in a position entirely exposed to the weather. This has the disadvantage that the antenna is subjected durin flight to mechanical stresses caused by air flow past the antenna. There is the further disadvantage that such exposed antennas become covered with dirt and may become coated with a film of condensation or a layer of ice, all of which conditions, substantially reduce the antenna efficiency. For example, a film of moisture on the antenna accelerates corrosion of the antenna surfaces thus mechanically to weaken the antenna. A deposit of ice on the antenna conductor may seriously change the antenna impedance and thereby impair the desired impedance matching between the antenna, an associated transmission line which couples the antenna to a wave-signal translating apparatus, and the output circuit of a transmitting apparatus or the input circuit of a receiving apparatus. A deposit of ice on the antenna-supporting insulators likewise tends to change the antenna impedance and, additionally, tends to impair the desired insulating qualities of the insulators for high wave-signal potentials. Deposits of dirt on the insulating support members for the antenna may cause substantial losses of wave-signal power.

To avoid these disadvantages of the exposed antenna, it has been proposed that the antenna be enclosed within a housing of insulating material secured to or forming a part of the aircraft structure. The forms of antenna housings heretofore proposed cannot readily be hermetically sealed, to protect the antenna from dirt, moisture and ice, without introducing severe problems which relate largely to the mechanical design of the housing and arise by virtue of the wide range of variations of pressure encountered in the operation of high altitude aircraft. The enclosed type of antenna systems heretofore suggested consequently are so constructed that one. or more openings are provided to connect the interior of the housing to the surrounding atmos phere. While this housing protects the antenna itself from mechanical stresses due to air flow past'the antenna during flight, the exchange of 5 air between the interior of the housing and the outside atmosphere with pressure and temperature variations causes dirt and moisture to be drawn into the housing where they may readily form an undesirable deposit on the antenna and its insulating support members.

It is an object of the present invention to provide a new and improved antenna system which avoids one or more of the disadvantages and limitations of prior antenna systems of the type described.

It is an additional object of the present invention to provide anew and improved antenna system, particularly suited for use with aircraft, which possesses uniformly high efliciency and a high degree of stability of its electrical characteristics at all usual altitudes and temperatures encountered.

It is a further object of the invention to provide a new and improved antenna system having an antenna conductor enclosed within a protective housing which, while hermetically sealed, has an automatically maintained condition of substantial equilibrium between the pressure within the housing and the surrounding outside atmospheric pressure even with substantial changes of the latter, so that excessive mechaniential are avoided.

'It is an additional object of the invention to provide an antenna system having an antenna enclosed withina hermetically sealed housing filled with a gas which is maintained at a uniformly low percentage of humidity at all times.

In accordance with one form of the invention, an antenna system comprises an antenna, a nonconductive relatively rigid housing enclosing the antenna, and means for hermetically closing the housing and including at least one portion pro viding a chamber wall exposed to atmospheric pressure and movable in response to variations drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, the single figure thereof is a sectional elevation illustrating the construction of an antenna system embodying the present invention.

Referring now more particularly to the drawing, there is illustrated an antenna system embodying the present invention in .a particular form. This system includes an antenna I and a nonconductive relatively rigid housing or envelope II enclosing the antenna and hermetically sealed except for an equalizing port I2 in one wall I3 thereof. The housing II preferably is of molded plastic, a transparent plastic being preferred to permit the inspection of the interior of the housing without the necessity of opening it up. The interior of the housing I I has sufficient capacity to provide a substantial air space all the way around the antenna III in order that the distributed capacitance of the latter shall be established primarily by the dielectric constant of the gas medium which fills the interior of the housing. The term gas" as used in the present.

specification is intended to include the usual inert gases, for example, nitrogen or carbon dioxide, and also to include air. The housing II is usually positioned on the exterior surface of an airplane wing or fuselage It and is preferably streamlined in cross section to minimize the resistance to the flow of air around its exterior surface.

The antenna system also includes hermetically sealed means, comprising an elastic balloon M, hermetically sealed to the housing II and having an internal chamber to connecting with the port E2, in a manner presently to be explained in greator detail, to permit the free passage of gas between the interior of the housing ii and the cl'iamber iii. Essentially, the last-mentioned means comprises means having at least one mova- "ole chamber wall exposed to atmospheric pressure and. movable in response to changes thereof to vary the volume of the chamber, thereby to reduce the pressure differential between the gas pressure within the housing ii and the atmospheric pressure outside it which would otherwise occur with decreases of atmospheric pressun. The balloon to is of flexible and especially elastic material, preferabh an elastomer. such as one of the buna rubber family, a modified butadiene acrylonitrile copolymer. a chloroprene polymer. or an organic polvsu nhide. All of these materials of the artificial rubber type and possess the ability to retain their elastic characteristics at the tem eratures prevailin at altitudes of 30,006 to 56.000 feet above sea level.

Theentenna it: is of an elongated form, for 6 example a quarter-wave vertical antenna. and is sup orted at its ends it and it by insulating members iii and Zili. respectively, provided at the too and bottom portions of the housing as indi cated. A coaxial connector 2 extends from the lower end of the antenna and projects externally through a side wall of a cup-shaped sub-housing 22 to permit the antenna to be coupled through a coaxial transmission line to an external wavesignal apparatus, not shown.

lhe balloon to has a neck 23 which is attached to a nipple lit provided on one wall of a hollow housing 26 positioned in the sub-housing 2? The latter has an interior chamber 27 connected with the equalizing port is through a tube ti}, The

housing 23 is filled with a hygroscopic substance 3I, such as silica gel, which serves to reduce by absorption the moisture content of the gas filling the interior of the housing I I and balloon I4.

A perforated basket 30 which may be of a plastic material is attached to the sub-housing 22 in any suitable manner to protect the balloon I4. Free access of the atmosphere to the exterior surface of the balloon I4 is provided by perforations in the walls of the basket 30.

A collar 32 surrounds a flared base portion of the housing I I, an insulating ring 33, a gasket 34 provided hermetically to seal the housing II and its wall member I3, and the sub-housing member 22. Machine screws 35 maintain the elements last-mentioned in assembled relation as a unitary' structure and secure the assembly to the airplane wing or fuselage I6.

Consider now the operation of the antenna system just described. The interior of the housing I I, the interior 21 of the housing 26 and chamber I5 of the balloon I4 are usually filled with gas at normal atmospheric pressure at the time of assembly of the antenna system. When the enclosed gas is air, this simply means that no attempt is made to evacuate the air at the time of assembly. The balloon I4 is preferably collapsed at the time of assembly. After assembly, any internal pressure within the housing II exceeding that of the surrounding atmospheric pressure, such as during flight of an airplane to high altitudes, results in an expansion of the gas within the housing II to inflate the balloon I4. This expansion of the gas within the system to inflate the balloon I4 is effective to maintain a substantial balance between the air pressureswithin and without the housing I I so that no injurious stress will be exerted on the latter. As the gas flows in both directions between the chambers of the housing H and balloon M, it passes through the intervening compartment 2i and thus passes through the silica gel or other hygroscopic substance 3%. This substantially dehumidifies the enclosed gas.

The antenna Ill operates in conventional manner to receive or radiate wave signals.

The balloon to preferably has a wall thickness limited to about one thirty-second of an inch maximum to minimize the gas or air pressure re quired to inflate it. This thickness has been em piricaliy established and provides an adequate factor of safety while at the same time affording ample flexibility and elasticity.

The use of silica gel treated with cobalt chloride is desirable from the standpoint that the color of the hygroscopic substance Iii varies with the moisture content thereof. Since clear plastic may be used for the housing 26 and sub-housing 22, the indications provided by such coloring can be readily observed at such times as may be desired.

From the above description of the invention, it will be apparent that the balloon Ed, the housing 26, and the tube 2% comprise means for hermetically closing the housing ii and including at least one portion, namely the balloon E i, providing a chamber wall exposed to atmospheric pressure and movable in response to variations thereof. It will further be apparent that the means lastmentioned provides with the housing II a hermetically sealed container having a portion, namely the housing Ii and housing 25, of constant volume and a portion, namely the balloon fications may be made therein without depart-- would otherwise occur with decreases of atmospheric pressure, and a hygroscopic substance in contact with said gas for reducing the moisture content of the gas filling the interior of said container. v

5. An .antenna system comprising, an antenna,

a nonconductive relatively rigid housing enclosing said antenna and hermetically sealed except for an equalizing port in one wall thereof, and

hermetically sealed means hermetically sealed to said housing'and including a chamber coning from the invention, and it is, therefore,"-

aimed in the appended claims to cover all such changes and modifications as fall within th'etrue spirit and scope of the invention.

What isclaimedis: 1. An antenna system comprising, an antenna,

a nonconductive relatively rigid housing enclos-.'

ing said antenna, and means for hermetically closing said housin and including at least one portion providing a chamber wall exposed to atmospheri'c pressure and movable in response to variations thereof, said means providing with said housing a hermetically sealed container having a portion of constant volume and a {may tion of volume variable withatmospheric pressure to reduce the pressure difierential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases pheric pressure.

2. An antenna system comprising; an antenna, a nonconductive relatively rigid housing enclosing said antenna, and means for hermetically closing said housing and including 'at least one portion providing a chamber wall of flexible conatmospheric pressure.

necting with said port to ,permit the free passage of gas between said chamber and the interior of said housing, said means having at least one movable chamber wall exposed to atmospheric pressure and movable in response to changes thereof to vary the volume of said chamber, thereby to reduce the pressure differential between the gas pressure within said housing and i the atmospheric pressure without said housing which would otherwise occur with decreases of v 6. 'An antenna system comprising, an antenna,

a nonconductive relatively rigid housing'enclosing. said antenna and hermetically sealed except for an equalizing port in one wall thereof, and

hermetically sealed means hermetically sealed to said housing and including a chamber connectstructionexposed to atmospheric pressure and movable in response to variations thereof,'said means providing with said housing a hermetically sealed container having a portion of constant volume and a portion of volume variable with atmospheric pressure to reduce the pressure differential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases of atmosperic pressure.

3. An antenna system comprising, an antenna,

a. nonconductive relatively rigid housing enclosing said antenna, and means for hermetically closing said housing and including at least one portion providing a chamber wall of elastic materlal exposed to atmospheric pressure and movable in response to variations thereof, said means providing with said housing a hermetically sealed container having a portion of constant volume and a portion of volume variable with atmospheric pressure to reduce the pressure difierential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur. with decreases of atmospheric pressure.

4. An antenna system comprising, an antenna, a nonconductive relatively rigid housing enclosing said antenna, means for hermetically closing said housing and including at least one portion providing a chamber wall exposed to atmospheric pressure and movable in response to variations thereof, said means providing with said housing a hermetically sealed container having a portion of constant volume and a portion of volume variable with atmospheric pressure to ing with said port to permit the free passage of gas between said chamber and the interior of said housing, said means having at least one movable chamber wall of flexible material which retains its flexibilityat high altitudes and is exposed toatmospheric pressure for flexible movement in response to changes thereof to vary the volume of said chamber, thereby to reduce the pressure differential'between the gas pressure within said housing andthe atmospheric pressure without said housing which would otherwise occur with decreases of atmospheric pressure.

'7. An antenna system comprising, an antenna, a, nonconductive relatively rigid housing enclosing said antenna and hermetically sealed except for an equalizing port in one wall thereof, and a hermetically sealed elastic container hermetically sealed to said housing and providing a chamber connecting with said port to permit the free pas- I sage of gas between said'chamber and the interior of said housing, said container having at least a portion of its exterior surface exposed to atmospheric pressure and elastically movable in respouse to changes thereof to vary the volume of reduce the pressure differential between the gas I pressure within said housing and the atmos said chamber, thereby to reduce the pressure differential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases of atmospheric pressure.

8. An antenna system comprising, an antenna, a nonconductive relatively rigid housing enclosing said antenna and hermetically sealed except for an equalizing port in one wall thereof, and

with said port to permit the free passage of gas between said chamber and the interior of said housing, said means having at least one movable chamber wall formed of one of the elastomers and exposed to atmospheric pressure for elastic movement in response to changes thereof to vary the volume of said chamber, thereby to reduce the pressure differential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases of atmospheric pressure.

9. An antenna system comprising, an antenna, a nonconductive relatively rigid housing enclosing said antenna and hermetically sealed except for an equalizing port in one wall thereof, and a hermetically sealed container formed of one of the elastomers and hermetically sealed to said housing for providing a chamber connecting with said port to permit the free passage of gas between said chamber and the interior of said housing, said container having at least a portion of its exterior surface exposed to atmospheric pressure and elastically movable in response to changes thereof to vary the volume of said chamber, thereby to reduce the pressure differential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases of atmospheric pressure. s

10. An antenna system comprising, an antenna, a nonconductive relatively rigid housing enclosing said antenna and hermetically sealed except for an equalizing port in one wall thereof, hermetically sealed means hermetically sealed to said housing and including a chamber connecting with said port to permit the free passage of gas between said chamber and the interior of said housing, said means having at least one movable chamber wall exposed to atmospheric pressure and movable in response to changes thereof to varyv the volume of said chamber, thereby to reduce the pres sure difierential between the gas pressure within said housing and the atmospheric pressure without said housing which would otherwise occur with decreases of atmospheric pressure, and a ygroscopic substance located between the interior of said-housing and said chamber in the path of gas passing therebetween for reducing the moisture content of the gas filling the interior of said housing.

WILLIAM M. HURST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS Number Name Date 2,167,201 Dallenba-ch July 25, 1939 1,227,404 DuBois May 22, 1917 1,495,010 Ford May 20, 1924 2,147,108 Rylsky Feb. 14, 1939 2,315,049 Cronstedt Mar. 30, 1943 

